1. Field of the Invention
The present invention relates to a communication system and an optical transmission device, and particularly to an effective technique applied to a communication system to realize redundancy in communication between optical transmission devices and an optical transmission device thereof.
2. Description of the Related Art
For example, U.S. Pat. No. 7,701,847 B2 discloses a system including a transmitting part that divides a transmission signal into two signals by a coupler and transmits the respective transmission signals through two cards, and a receiving part that receives the respective transmission signals through two cards and combines the received signals by a coupler. In the receiving part, the qualities of the received signals are compared between the two cards, and one of the cards which is more excellent in quality is selected.
For example, in a communication network of a company, there is a case where a large amount of data are transmitted and received between, for example, bases separated from each other by several tens km or more in the company. Especially, in such a communication network, it is required that a communication band is expanded and the distance of communication is extended. In order to satisfy such a request, for example, a technique is known in which a device called an optical transmission device is placed in each of the bases in the company, and the respective optical transmission devices are connected to each other by long-distance optical fiber cables.
In such a communication network, since the number of optical fiber cables to connect the optical transmission devices is limited in view of the cost, in the optical transmission device, a technique to expand the communication band of each optical fiber cable is developed. On the other hand, when the long-distance optical fiber cable is used, a possibility that a failure occurs in the cable becomes high. As a result, when such a failure occurs, the damage becomes large.